Constant current series regulator with control of bias current energizing control circuit of the regulator

ABSTRACT

The regulation of the current output of a series type current regulator is significantly improved by closely regulating the bias currents required by the control and reference elements of the regulator. These regulated bias currents may be coupled to the output circuit and form part of the output load current. The regulated bias currents are utilized to energize a reference voltage source and a voltage comparison circuit which in turn control the series regulating device of the current regulator.

United States Patent [1 1 Healey et al. [451 Mar. 28, 1972 CONSTANTCURRENT SERIES [56] References Cited REGULATOR WITH CONTROL OF BIASUNITED STATES PATENTS CURRENT ENERGIZING CONTROL 3,434,038 3/1969Vette.- .323/4 CIRCUIT OF THE REGULATOR Inventors: Robert Joseph Henley,Morris Township, Morris County; Helmut Stocker, Randolph Township,Morris County, both of NJ.

Appl. No.: 90,731

U.S. Cl ..323/4, 323/22 T, 323/38 Int. Cl. ..H02j 1/04, G05f1/56 Fieldoi Search ..323/4, 9, 22 T, 38

3,182,246 5/1965 Lloyd Primary ExaminerGerald Goldberg Att0rney-R. J.Guenther and E. W. Adams, Jr.

[57] ABSTRACT voltage source and a voltage comparison circuit which inturn control the series regulating device of the current regulator.

v 5 Claims, 3 Drawing Figures PATENTEDMAREB r972 3,652,922

FIG (PRIOR ART) FIG. 2 (PRIOR ART) MR V FIG. 3

(loo

R. J. HE ALE Y uvvawrms STOCKER ATTORNEY BACKGROUND OF THE INVENTIONThis invention relates to series regulators which supply a constantcurrent output. The invention is specifically 'concerned with theregulation and efficient utilization of the bias currents required bythe control and reference circuitry of the series regulator.

A typical constant current regulator, such as shown in FIG. 1, includesa breakdown diode l3, energized by an input power source coupled to theinput terminals 1 and 2, to derive a reference voltage utilized tocontrol the regulator. The regulated output current is transmittedthrough the series regulator transistor 20 and a current sensingresistor 11 to an output load 100. The reference voltage developedacross the breakdown diode 13 controls the emitter-to-base voltage ofthe transistor 20. It is apparent from examination of the circuit inFIG. 1 that the transistor 20 transmits a current having a controlledmagnitude which maintains the voltage across the current sensingresistor 11 proportional to the voltage across the breakdown diode 13.

This circuit, while simple in operation and reliable, is limited in theprecision of regulation it can achieve. The portion of the input currentutilized to energize the breakdown diode 13 is directly transmitted tothe load 100. The current energizing the breakdown diode 13 isunregulated since it bypasses the current sensing resistor 11. Hence theoutput current supplied to the load 100 tends to vary in response tochanges in the input voltage applied to input terminals 1 and 2 and tochanges in the output load 100.

Another typical constant current regulator of the prior art is shown inFIG. 2. In this regulator the breakdown diode 13, which establishes thereference voltage, shunts the input terminals I and 2. Hence the currentenergizing the breakdown diode l3 bypasses the output load 100 and doesnot adversely affect the precision of regulation. This regulationarrangement is less efficient than the regulation disclosed in FIG. 1.The current which energizes the breakdown diode 13 is dissipated anddoes not contribute to the output load current.

It is, therefore, an object of the invention to improve the precision ofregulation of a series current regulator by regulating the bias currentenergizing the reference voltage breakdown diode.

' It is another object of the invention to maintain a constant outputcurrent in a series regulator essentially independent of changes in theinput voltage or changes in the output load.

It is yet another object of the invention to improve the efficiency of aseries current regulator by utilizing the regulated bias currents aspart of the load current.

SUMMARY OF THE INVENTION The above enumerated objects are achieved inthe invention by regulating the currents utilized to energize the seriesregulating transistor and the breakdown diode which,

transistor by draining the bias current in excess of its require-v mentfrom its control electrode. The excess bias current is transmitted tothe current sensing resistor and forms part of the regulated outputcurrent.

The current energizing the breakdown diode is regulated to significantlylimit its detrimental effect on the precision of regulation. Thebreakdown diode current is regulated by a control transistor and acurrent measuring resistor. .T he current measuring resistor shunts thebase-emitter junction of the control transistor which junction voltagein turn controls the voltage drop across the measuring resistor. Thecurrent through the current measuring resistor is proportional andessentially equal to the current through the breakdown diode.

The current measuring resistor hence regulates the current energizingthe breakdown diode.

The current traversing the collector-emitter path of the controltransistor is advantageously limited by coupling the collector of thetransistor to the base electrode ofthe current bypass transistor. Thisadvantageously limits the unregulated bias current transmitted to theoutput load of the series current regulator.

DESCRIPTION OF THE DRAWINGS In the drawings, FIG. I is a schematicdiagram of a typical constant current regulator existing in the priorart and described hereinabove;

FIG. 2 is a schematic diagram of a typical constant current regulatorexisting in the prior art also described hereinabove and which has agreater precision of regulation and less efficiency than the regulatorshown in FIG. 1; and

FIG. 3 is a schematic diagram of a constant current series regulatorembodying the principles of the invention to improve the precision ofregulation of the output current and more efficiently utilize the biascurrent energizing the control circuitry.

DETAILED DESCRIPTION OF THE INVENTION A current regulator, as shown inFIG. 3', embodying the principles of the invention regulates a currentsupplied by an input voltage source coupled to the input terminals 1 and2. This regulated current is controlled by two compound connected seriesregulating transistors 10 and 20. The combined transconductive impedanceof transistors 10 and 20 is controlled in response to a voltagegenerated across the current sensing resistor 55. A current bypasstransistor 40 responsive to the regulation control circuitry controlsthe bias current applied to the series regulating transistors 10 and 20by draining controlled amounts of current away from the controlelectrode 22. This excess drained current is transmitted to the currentsensing resistor 55 and forms part of the regulated output load current.

The invention may be explained by describing the operation of the seriescurrent regulator shown in FIG. 3. In the operation of this circuit, aDC voltage source is coupled to the input terminals 1 and 2. A portionof the input current from this source is applied to the collector 13 andthe collector 23 of the series regulating transistors 10 and 20,respectively. A portion of the input current is also transmitted, viathe resistor 51, to base electrode 22. This signal biases the compoundconnected transistors 10 and 20 into a conductive state. The outputcurrent traversing the transconductive path of transistors 10 and 20flows through the current sensing resistor 55. The voltage drop acrossthe current sensing resistor 55 is directly proportional to the combinedcurrent flow through the transconductive paths of transistors 10 and 20.

A portion of the input current is also applied via resistor 51 and thetransconductive or collector-emitter path of the current bypasstransistor 40 to a reference voltage breakdown diode l5 and to thecurrent sensing resistor 55. A portion of the input .current is alsoapplied via resistor 51 and the emitter-base path of transistor 40 44the control transistor 30. The transistor 30 in response to this currentdevelops a substantially constant voltage across its base-emitterjunction. A current measuring resistor 50 shunts the base-emitterjunction of transistor 30 and is connected in series with the breakdowndiode 15. The bias current energizing the breakdown diode 15 isregulated by the controlled voltage drop across the resistor 5 Thecurrent energizing the breakdown diode 15 is applied to the output 'load100. This bias current may be advantageously optimized to operate thebreakdown diode 15 in its most stable region. The current traversing thecollectoremitter path of transistor 30 is supplied via the emitter-basejunction of transistor 40. This particular connection minimizes thecurrent flowing through transistor 30 and hence reduces the unregulatedbias current transmitted to the 100.

It is apparent from the foregoing that the main component of the loadcurrent supplied to the output load 100 is derived from currenttransmitted by the regulating transistors and 20 and from currenttransmitted by the current bypass transistor 40. The current transmittedby the current bypass transistor 40 is applied in parallel to thecurrent sensing resistor 55 and the breakdown diode 15. The currentapplied to the current sensing resistor 55 becomes part of the regulatedload current. The current traversing the breakdown diode is regulated bythe voltage drop across the current measuring resistor 50 controlled bythe base-emitter junction voltage of transistor 30. This current isapplied to the load 100. Since the current traversing the breakdowndiode 15 is regulated, the total output current applied to the outputload 100 is very precisely regulated.

The transconductive impedance of transistors 10 and is regulated to keepthe current flow therein constant. If, for example, the load currentincreases, the voltage drop across the current sensing resistor 55increases in response thereto. This increase in voltage increases thecurrent flowing into the base 31 of the control transistor 30. Thisincreased current biases transistor 30 into a higher conductive stateand increases the base current of the current bypass transistor 40. Thecurrent bypass transistor 40 is biased into an increased state ofconductivity and due to this increased conduction shunts current awayfrom the base 22 of the transistor 20. The transconductive impedance oftransistors 10 and 20 is accordingly increased, reducing the currentoutput at the emitter 11. This reduces the load current applied to theoutput load 100 to its regulated value. It is apparent that if theregulated current output at emitter 11 decreases, the voltage across thecurrent sensing resistor 55 will decrease and the converse regulationwill operate to increase the load current to its regulated value.

The temperature stability of the regulator may be advantageouslyimproved by selecting a breakdown diode 15 with temperaturecharacteristics complementary to the temperature characteristics of thebase-emitter junction of transistor 30. In this instance a breakdowndiode 15 should have a positive temperature characteristic wherein itsvoltage drop increases with temperature in order to counteract thenegative temperature characteristic of the base-emitter junction. Thistemperature compensation scheme improves the precision of regulation ofthe regulator with respect to temperature changes.

The resistor 53 shunting the collector-emitter path of transistorl0 isincluded to limit the power dissipation of the series regulatingtransistors 10 and 20 to a safe value should the voltage increasesignificantly. The resistors 52 and 54 are utilized as collector-baseleakage path resistors for the transistor 40 and the transistor 10,respectively. These leakage paths help to provide thermal stability forthe operation of the regulator within the normal temperature range inwhich the circuit operates. The feedback capacitor 61 is included tomodify the gain phase characteristics of the series regulator to preventhigh frequency instability problems. The diodes 25 and 35 are includedas protection against high voltage surges such as may be caused bylightning striking the load.

lt is understood that the principles of the invention are equallyapplicable if semiconductor devices of an opposite polarity from thosedescribed are used. Such a substitution may involve designing aregulator utilizing PNP-transistors inoutput load stead ofNPN-transistors as disclosed herein.

We claim:

l. A constant current supply comprising input and output terminals, avariable impedance current regulator including a control electrode, acurrent sensing impedance connected in series with said currentregulator, a bias current path connecting one of said input terminals tothe control electrode of said current regulator, semiconductor breakdownmeans to establish a reference voltage, means to compare the voltagedrop across said current sensing imlpedance with said reference voltageincluding a contro transistor, means responsive to said means to compareto adjust the impedance of said variable impedance current regulatorincluding a current bypass transistor, the collector-emitter path ofsaid current bypass transistor connecting said control electrode to ajunction of said current regulator and said current sensing impedance,the collector-emitter path of said control transistor connecting thebase electrode of said current bypass transistor to a junction of saidcurrent sensing impedance and said output terminal, said semiconductorbreakdown means being connected across the series connection of thecollector base junction of said control transistor and the collectorbase junction of said current bypass transistor, whereby said bypasstransistor controls the bias current applied to said control electrodeand transmits the excess bias current supplied by said bias current pathto one of said output terminals via said current sensing impedance.

2. A constant current supply as defined in claim 1 further including acurrent limiting resistor in series with said semiconductor breakdownmeans and being shunted across the base emitter junction of said controltransistor.

3. A constant current supply asdefined in claim 2 wherein said variableimpedance current regulator comprises a plurality of compound connectedtransistors.

4. A current regulator comprising a series regulating device including atransconductive path and a control electrode to receive signals tocontrol the conductivity of said transconductive path, a current pathcomprising a transistor with a controllable transconductive impedance todivert bias signals from said control electrode in order to control thetransconductive impedance of said series regulating device, a currentsensing device to generate a voltage proportional to the currenttransmitted by said series regulating device, a source of referencevoltage comprising a current energized breakdown diode, a comparisoncircuit to compare the reference voltage and the voltage generated bysaid current sensing device, said comparison circuit being coupled toand controlling the trans conductive impedance of the transistor of saidcurrent path, said comparison circuit comprising means to regulate thecurrent energizing said source of reference voltage including a secondtransistor and a current drain control impedance whose voltage drop iscontrolled by the base-emitter junction voltage of said secondtransistor, said current drain control impedance being in series withsaid source of reference voltage, and the collector base of saidtransistor in said current path and the collector base of said secondtransistor being series connected with said reference voltage source ina closed loop whereby the current absorbed by said second transistor islimited.

5. A current regulator as defined in claim 4 wherein said breakdowndiode has a temperature characteristic complementary to the temperaturecharacteristic of the base-emitter junction of said second transistor.

1. A constant current supply comprising input and output terminals, avariable impedance current regulator including a control electrode, acurrent sensing impedance connected in series with said currentregulator, a bias current path connecting one of said input terminals tothe control electrode of said current regulator, semiconductor breakdownmeans to establish a reference voltage, means to compare the voltagedrop across said current sensing impedance with said reference voltageincluding a control transistor, means responsive to said means tocompare to adjust the impedance of said variable impedance currentregulator including a current bypass transistor, the collector-emitterpath of said current bypass transistor connecting said control electrodeto a junction of said current regulator and said current sensingimpedance, the collectoremitter path of said control transistorconnecting the base electrode of said current bypass transistor to ajunction of said current sensing impedance and said output terminal,said semiconductor breakdown means being connected across the seriesconnection of the collector base junction of said control transistor andthe collector base junction of said current bypass transistor, wherebysaid bypass transistor controls the bias current applied to said controlelectrode and transmits the excess bias current supplied by said biascurrent path to one of said output terminals via said current sensingimpedance.
 2. A constant current supply as defined in claim 1 furtherincluding a current limiting resistor in series with said semiconductorbreakdown means and being shunted across the base emitter junction ofsaid control transistor.
 3. A constant current supply as defined inclaim 2 wherein said variable impedance current regulator comprises aplurality of compound connected transistors.
 4. A current regulatorcomprising a series regulating device including a transconductive pathand a control electrode to receive signals to control the conductivityof said transconductive path, a current path comprising a transistorwith a controllable transconductive impedance to divert bias signalsfrom said control electrode in order to control the transconductiveimpedance of said series regulating device, a current sensing device togenerate a voltage proportional to the current transmitted by saidseries regulating device, a source of reference voltage comprising acurrent energized breakdown diode, a comparison circuit to compare thereference voltage and the voltage generated by said current sensingdevice, said comparison circuit being coupled to and controlling thetransconductive impedance of the transistor of said current path, saidcomparison circuit comprising means to regulate the current energizingsaid source of reference voltage including a second transistor and acurrent drain control impedance whose voltage drop is controlled by thebase-emitter junction voltage of said second transistor, said currentdrain control impedance being in series with said source of referencevoltage, and the collector base of said transistor in said current pathand the collector base of said second transIstor being series connectedwith said reference voltage source in a closed loop whereby the currentabsorbed by said second transistor is limited.
 5. A current regulator asdefined in claim 4 wherein said breakdown diode has a temperaturecharacteristic complementary to the temperature characteristic of thebase-emitter junction of said second transistor.